A 100 Pico farad capacitor is charged to a potential difference of 100 volt . it is connected in parallel to another capacitor final voltage 30volt then what will be capacitance of second capacitor . how much energy is wasted in it

Let’s apply the capacitor's equation:

Q = C . V

▶Where Q is the charge, C the capacitance, and V the voltage.

Q0 = C0 . V0, where C0 is 100pF and V0 is 100V

▶When we connect the capacitors in parallel, we equal the voltage on the two, therefore:

V = Q / C ==> Q0′/C0 = Q1/C1

▶Where Q0' is the charge on the 100pF capacitor after connecting the other one, and Q1 and C1 the homologous.

We also know that the total charge is conserved, so:

Q0 = Q0' + Q1

And we know that Q0' = C0 . V1, where V1 = 30V

♦We have three equations and three unknowns Q0', Q1, and C1. You can go ahead and solve it and then punch in the values of the constants.